Astronauts make last spacewalk of NASA shuttle era

By MARCIA DUNN | July 12, 2011 | 9:44 AM EDT

In this Sunday, July 10, 2011 photo provided by NASA, the space shuttle Atlantis is seen over the Bahamas prior to a perfect docking with the International Space Station. Part of a Russian Progress spacecraft which is docked to the station is in the foreground. (AP Photo/NASA)

CAPE CANAVERAL, Fla. (AP) — The last spacewalk of NASA's space shuttle era is under way nearly 250 miles above Earth.

They'll retrieve a broken ammonia pump outside the International Space Station and pack it aboard the docked shuttle Atlantis. NASA wants the pump brought back so engineers can figure out why it failed last summer. The two will also set up a robotic refueling experiment.

Only four astronauts are flying Atlantis. It's the smallest crew in decades — too small, in fact, to have had time to train for this spacewalk. That's why the job was handed over to the space station crew.